Measurements of Forces Involved in Vesicle Adhesion Using Freeze-Fracture Electron Microscopy

Vesicle adhesion was investigated by freeze-fracture electron microscopy. Membrane stresses were imposed by osmotic gradients to assess the relative importance of repulsive thermal undulation and attractive hydrophobic forces on vesicle membrane interactions. The adhesion energy was found to be proportional to the membrane tension, but its magnitude could not be explained from quenching undulation forces since the adhesion energy rose to well above the maximum possible van der Waals contribution. The increased adhesion energy was the result of increased hydrophobic interactions, which result whenever bilayers are stretched so that their hydrocarbon interiors become more exposed to the aqueous phase.